This invention relates to apparatus and method for growing epitaxial layers of compound semiconductor material on a compound semiconductor substrate using Metal Organic Chemical Vapor Deposition techniques.
At present, epitaxial layers for enhancement mode (Emode) HIGFET devices are grown directly on a substrate using the molecular beam epitaxy (MBE) process with only a GaAs buffer layer. MBE epitaxial growth is slow and expensive, which severely limits the quantity of available material and substantially adds to the cost of devices.
Attempts to grow Emode devices by the faster and cheaper Metal Organic Chemical Vapor Deposition (MOCVD) process have not been successful. Previous MOCVD-grown Emode devices have had poor repeatability and often high leakage currents, so high that they are unusable. Some success has been realized in the growth of depletion-mode FETs using MOCVD. See for example an article by N. Pan et al., J. Electron, Mat. 21, 199 (1992) and an article by Sasajima et al., xe2x80x9cHigh Resistivity Oxygen-Doped AlGaAs for Power Devicesxe2x80x9d, Proc. of MRS, November 1997. However, it is commonly believed in the art that Emode HIGFET devices cannot be successfully grown by the MOCVD process.
Accordingly, it is highly desirable to provide Emode HIGFET devices by the MOCVD process and to provide a new method of forming high performance Emode epitaxial structures by the MOCVD process. Fabricating epitaxial layers of Emode devices using the MOCVD process will permit cost reduction and ensure an adequate supply of device-quality material.